Science Behind Food Canning
Microorganisms such as yeasts, molds and bacteria are invisible to our eyes and are present all around us. Some of these microorganisms are beneficial, and some others are harmful. To a certain extent, nearly all foods contain some of these microorganisms. It is these microorganisms though that will make food spoil. So, If you don’t properly preserve your food, it will undergo change in color and flavor and eventually decompose because of the growth of these microorganisms.
Canning helps to prevent the growth of microorganisms by heating food in a sealed container. Heat not only destroys the harmful microorganisms, but it also drives the air out and creates a partial vacuum inside the container. This prevents re-contamination of the food as other microorganisms cannot enter vacuum-sealed containers.
Two Different Kinds Of Food
For canning purposes, there are two types of food: High-Acid and Low-Acid foods.
- High-Acidic Foods: These are foods that consist of natural acids in them. The acidity of each food may vary. In general, fruits, including tomatoes, are classified as acid foods.
- Low-Acidic Foods: These foods contain very low levels of natural acids. Typically, vegetables, meats, seafood, mushrooms, poultry and soups are classified as being low-acid foods. Mixed canned foods that contain both acid and low-acid foods are generally considered to be low-acid foods.
Science of Food Preservation
It is easy to preserve high acidic foods by canning. This is because yeasts and molds that thrive in acids can be easily destroyed by heating containers filled with food in boiling water for a certain amount of time. The natural acids present in food, and heating is sufficient in gets acid foods. However, some bacteria thriving in low-acid foods are not destroyed by the temperature of boiling water. Processing refers to the heating of food within closed containers. If the food to be canned is not processed at the correct temperature for the right amount of time, it gets spoiled. This is because improper processing fails to destroy all the microorganisms present in food. Additionally, you may not achieve proper sealing to prevent the entry of microorganisms that cause spoilage as well as food-borne illnesses.
What Causes Food To Spoil?
Fungi such as yeasts and molds are able to be destroyed when they are subjected to 140 degrees to 190 degrees Fahrenheit temperatures. However, bacteria cannot be destroyed that easily as some bacteria are capable of thriving at the temperatures that kill yeasts and molds.
If the temperature is maintained at 140 degrees Fahrenheit, salmonella bacteria can be killed. For destroying Staphylococcus aureus bacteria, you need to raise the temperature beyond 140 degrees Fahrenheit. However, to destroy the toxin produced by this bacterium you need to boil the food for long hours or superheat it to 240 degrees Fahrenheit for a relatively shorter period. The bacterium clostridium botulinium exists in food in the spore form. If the spores are not destroyed at the time of processing food, they multiply and produce a powerful poison. Heating the food to a temperature of 212 degrees Fahrenheit (boiling point of water) will not destroy these spores or the toxin. Additionally, these bacteria thrive well on low-acid foods, especially in moist environment and in the absence of air. This is same as the condition that prevails inside the jars of canned vegetables or meat. It is because of this reason that low-acid foods are heated to 240 degrees Fahrenheit, which is higher than the temperature at which water boils.
Two Canning/Processing Methods
Boiling Water Method: With this method a boiling water canner can be used for processing acid foods. With a boiling water canner you use a kettle that allows you to place the canning jar under water. There should be at least one or two inches of water above the jar and the kettle should be of sufficient size to permit a rolling boil.
Typically, boiling water canners come with tight-fitting covers and metal racks or baskets that prevent the jars from touching each other and the bottom of the kettle. The jars are held off the bottom to ensure proper heat penetration and prevent breakage.
Pressure Method: Steam pressure canners can be used for preserving low-acid foods. This type of canner consists of a heavy kettle and a steam-tight lid that is either locked or clamped down. The lid is also provided with a safety valve, petcock and a pressure gauge.
Two different types of commercial pressure scanners are available: those that are weighted and those that have dial gauges. It is important to check dial gauges to determine their accuracy as you want to be sure that they are operating at the right temperature. Because if they are not operating at the correct temperature all the bacteria, including botulism, may not be destroyed. The vent or petcock on pressure canners allows escape of steam in a regulated manner. If the petcock gets blocked inadvertently, the safety valve will pop to prevent the explosion of the kettle.
Safety Is Paramount
It is safe as well as efficient to process low-acid foods using pressure canning method as long as the canner remains clean and in proper working condition and processing is carried out under right temperature and pressure. In the event of any drop in pressure during canning, the process should be restarted from the beginning. You should also follow the instructions provided by the pressure canner manufacturer. Additionally, It is important to keep the pressure canner clean and in good working condition as both high pressure steam and under processed food can be dangerous. Ensure that nothing is obstructing either the petcock or the safety valve.
Don’t Cut Corners
The working principle of the pressure cookers or saucepans is similar to pressure canners, but they are generally smaller in size. Therefore, they cannot be used in place of pressure canners.